Plants face changes in leaves under lead (Pb) toxicity. Reduced glutathione (GSH) has several functions in plant metabolism, but its role in alleviating Pb toxicity in cotton leaves is still unknown. In the present study, cotton seedlings (28 days old) were exposed to 500 μM Pb and 50 μM GSH, both alone and in combination, for a period of 10 days, in the Hoagland solution under controlled growth conditions. Results revealed Pb-induced changes in cotton's leaf morphology, photosynthesis, and oxidative metabolism. However, exogenous application of GSH restored leaf growth. GSH triggered build up of chlorophyll a, chlorophyll b, and carotenoid contents and boosted fluorescence ratios (F v/F m and F v/F 0). Moreover, GSH reduced the malondialdehyde (MDA), hydrogen peroxide (H2O2), and Pb contents in cotton leaves. Results further revealed that total soluble protein contents were decreased under Pb toxicity; however, exogenously applied GSH improved these contents in cotton leaves. Activities of antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), and ascorbate peroxidase (APX)) were also increased by GSH application under Pb toxicity. Microscopic analysis showed that excess Pb shattered thylakoid membranes in chloroplasts. However, GSH stabilized ultrastructure of Pb-stressed cotton leaves. These findings suggested that exogenously applied GSH lessened the adverse effects of Pb and improved cotton's tolerance to oxidative stress.
Keywords: Lead; Metabolic changes; Reduced glutathione; Ultramorphology; Upland cotton.